There are two conventional types of pressure gauge that directly indicate values of fluid pressure applied to a gauge port: thus there is the Bourdon gauge and its derivatives, and like arrangements, in which pressure at a gauge port is applied to a containment element such as a bent tube, a capsule or a diaphragm to cause deformation of that element, an indicating mechanism linked to the element causing relative movement between an indicating element such as a pointer and a graduated scale in consequence of such deformation. The second conventional type of pressure gauge is the manometer and its derivatives, in which pressure at a gauge port is balanced by the hydrostatic pressure at the base of a liquid column so that the height of the column is a measure of the pressure at the gauge port.